trainer right join pokemon on pokemon.type = trainer.type에서 type이 electric인 데이터가 pokemon 데이터가 n개, trainer 데이터가 m개인 경우 어떻게 될까?
-> n*m + α 개의 데이터가 만들어진다.
(α: 포켓몬에만 존재하는 타입을 가진 데이터)

실험

1. 데이터 구성

pokemon

create table pokemon (
    id INT auto_increment primary key,
    name varchar(20),
    type varchar(20)
);

trainer

create table trainer (
	trainer_id BIGINT primary key,
    trainer_name varchar(20),
    trainer_type varchar(20)
);

pokemon data

id	name	type
1	pikachu	electric
2	balbusaur	grass
3	pikachu	electric
4	coil	electric

trainer data

trainer_id	trainer_name	trainer_type
1	ash	electric
2	martin	electric
3	hyuaryun	fire

2. 쿼리 실행

select * from trainer right join pokemon
on trainer.trainer_type=pokemon.type

3. 결과

trainer_id	trainer_name	trainer_type	id	name	type
1	ash	electric	1	pikachu	electric
1	ash	electric	3	pikachu	electric
1	ash	electric	4	coil	electric
2	martin	electric	1	pikachu	electric
2	martin	electric	3	pikachu	electric
2	martin	electric	4	coil	electric
NULL	NULL	NULL	2	bulbasaur	grass